The present invention relates to a packaging substrate such that electronic components are surface-mounted on the substrate, each electronic component having at side edge portions thereof a plurality of outwardly extending connecting terminals.
When surface mounting electronic components (for example, IC packages with external lead terminals attached thereto), each having at side edge portions thereof a plurality of outwardly extending connecting terminals, on a substrate in adjacent relation to each other, it has hitherto been a typical practice to dispose a plurality of connecting terminals generally uniformly at given intervals at side edge portions of each electronic component, and to arrange them so that the connecting terminals of adjacent electronic components are positioned in opposed relation.
Various proposals intended for packaging density improvement in surface mount of such electronic components on a substrate have been made. In Japanese Patent Laid-Open Publication HEI 2-68983 (hereinafter, referred to as prior art 1), for example, there is disclosed an improvement in the layout of external lead terminals of electronic components.
In this prior art 1, as shown in FIG. 4, at side edge portions of the body 71 of each electronic component 70 (IC module), there are provided a pin arrangement portion 71A at which a plurality of lead terminals 72 are arranged in a side-by-side fashion and a no-pin portion 71B at which no pin is present. When mounting such electronic components 70 adjacent to each other on a printed board (not shown), the electronic components 70 are usually laid out in such a way that pin arrangement portions 71A and no-pin portions 71B, in combination, are so disposed as to define a diagonally crossing configuration so that each pin arrangement portion 71A of each electronic component 70 and the opposite side no-pin portion 71B are positioned in opposed relation.
By employing such arrangement, it is possible to reduce the length of the space required in the longitudinal direction of leads for mounting the electronic component 70 as compared with the prior art case in which adjacent electronic components are disposed so that plural leads substantially uniformly arranged at given intervals on side edge portions of the electronic components are positioned in opposed relation. That is, it is possible to increase the packaging density of the electronic components on the substrate.
In the case of a so-called memory IC, for example, one bypass capacitor is required for each IC package. Therefore, when mounting such an IC package on a substrate, it is necessary that a bypass capacitor to be annexed to the IC package is mounted adjacent thereto.
Hitherto, when mounting such an IC package and a bypass capacitor on a substrate, as FIG. 3 (hereinafter, referred to as prior art 2) illustrates by way of example, it has been a common practice to dispose a plurality of lead terminals 62 generally uniformly at given intervals on side edge portions of the body 61 of each IC package 60, and to lay out adjacent IC packages 60, with a bypass capacitor disposed therebetween, so that leads 62 of the adjacent IC packages 60 are positioned in opposed relation.
With such a layout, however, it is necessary to provide a length of the space extending in the longitudinal direction of leads 62 (lateral direction in FIG. 3) which corresponds to a cumulative total of the length Lp of IC package 60 including a component mounting land 63, the length Lc of a bypass capacitor 66 including a land 67, and a clearance Ls of such an order as not to allow any inter-component electrical short circuit.
Therefore, the longitudinal size of the space required for mounting components in place on substrate 51, as viewed in the longitudinal direction of leads, (that is, packaging density on the substrate), are determined according to the size of components (such as package length Lp and capacitor length Lc). Therefore, any further improvement in packaging density has not been possible. In the above mentioned case, spaces left open at opposite end sides of bypass capacitor 66 which extend along side edge portions of adjacent package bodies 61 (in a vertical direction as viewed in FIG. 3) are useless unoccupied spaces.
It is to be noted that, according to above mentioned prior art 1, the packaging density of electronic component 70 (IC module) only can be improved. However, other kind of electronic component (such as capacitor) cannot be disposed between adjacent electronic components 70. As such, when mounting an electronic component having a plurality of connecting terminals at side edge portions, and other kind of electronic component to be mounted in combination therewith, as in the case of IC package and a bypass capacitor therefor, the prior art 1 is not effectively applicable.